This article documents the performance of the ATLAS muon identification and reconstruction using the LHC dataset recorded at
s
=
13
TeV in 2015. Using a large sample of
J
/
ψ
→
μ
μ
and
Z
→
μ
μ
...decays from 3.2 fb
-
1
of
pp
collision data, measurements of the reconstruction efficiency, as well as of the momentum scale and resolution, are presented and compared to Monte Carlo simulations. The reconstruction efficiency is measured to be close to
99
%
over most of the covered phase space (
|
η
|
<
2.5
and
5
<
p
T
<
100
GeV). The isolation efficiency varies between 93 and
100
%
depending on the selection applied and on the momentum of the muon. Both efficiencies are well reproduced in simulation. In the central region of the detector, the momentum resolution is measured to be
1.7
%
(
2.3
%
) for muons from
J
/
ψ
→
μ
μ
(
Z
→
μ
μ
) decays, and the momentum scale is known with an uncertainty of
0.05
%
. In the region
|
η
|
>
2.2
, the
p
T
resolution for muons from
Z
→
μ
μ
decays is
2.9
%
while the precision of the momentum scale for low-
p
T
muons from
J
/
ψ
→
μ
μ
decays is about
0.2
%
.
A
bstract
This paper describes a measurement of the
Z
/
γ
*
boson transverse momentum spectrum using ATLAS proton-proton collision data at a centre-of-mass energy of
s
=
7
TeV at the LHC. The ...measurement is performed in the
Z
/
γ
*
→
e
+
e
−
and
Z
/
γ
*
→
μ
+
μ
−
channels, using data corresponding to an integrated luminosity of 4.7 fb
−1
. Normalized differential cross sections as a function of the
Z
/
γ
*
boson transverse momentum are measured for transverse momenta up to 800 GeV. The measurement is performed inclusively for
Z
/
γ
*
rapidities up to 2.4, as well as in three rapidity bins. The channel results are combined, compared to perturbative and resummed QCD calculations and used to constrain the parton shower parameters of Monte Carlo generators.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The luminosity calibration for the ATLAS detector at the LHC during pp collisions at ... in 2010 and 2011 is presented. ...Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at ... A luminosity uncertainty of ... is obtained for the 47 pb^sup -1^ of data delivered to ATLAS in 2010, and an uncertainty of ... is obtained for the 5.5 fb^sup -1^ delivered in 2011.
Results of a search for new phenomena in events with at least three photons are reported. Data from proton–proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated ...luminosity of 20.3 fb
-
1
, were collected with the ATLAS detector at the LHC. The observed data are well described by the Standard Model. Limits at the 95 % confidence level on new phenomena are presented based on the rate of events in an inclusive signal region and a restricted signal region targeting the rare decay
Z
→
3
γ
, as well as di-photon and tri-photon resonance searches. For a Standard Model Higgs boson decaying to four photons via a pair of intermediate pseudoscalar particles (
a
), limits are found to be
σ
×
BR
(
h
→
a
a
)
×
BR
(
a
→
γ
γ
)
2
<
10
-
3
σ
SM
for 10 GeV
<
m
a
<
62 GeV. Limits are also presented for Higgs boson-like scalars (
H
) for
m
H
>
125 GeV, and for a
Z
′
decaying to three photons via
Z
′
→
a
+
γ
→
3
γ
. Additionally, the observed limit on the branching ratio of the
Z
boson decay to three photons is found to be BR
(
Z
→
3
γ
)
<
2.2
×
10
-
6
, a result five times stronger than the previous result from LEP.
A
bstract
A search for squarks and gluinos in final states containing high-
p
T
jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2012 by the ATLAS ...experiment in
s
=
8
TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 20
.
3 fb
−1
. Results are interpreted in a variety of simplified and specific supersymmetry-breaking models assuming that
R
-parity is conserved and that the lightest neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 1330 GeV for a simplified model incorporating only a gluino and the lightest neutralino. For a simplified model involving the strong production of first- and second-generation squarks, squark masses below 850 GeV (440 GeV) are excluded for a massless lightest neutralino, assuming mass degenerate (single light-flavour) squarks. In mSUGRA/CMSSM models with tan
β
= 30,
A
0
= −2
m
0
and
μ >
0, squarks and gluinos of equal mass are excluded for masses below 1700 GeV. Additional limits are set for non-universal Higgs mass models with gaugino mediation and for simplified models involving the pair production of gluinos, each decaying to a top squark and a top quark, with the top squark decaying to a charm quark and a neutralino. These limits extend the region of supersymmetric parameter space excluded by previous searches with the ATLAS detector.
This Letter presents evidence for single top-quark production in the s-channel using proton–proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS detector at the CERN Large Hadron ...Collider. The analysis is performed on events containing one isolated electron or muon, large missing transverse momentum and exactly two b-tagged jets in the final state. The analysed data set corresponds to an integrated luminosity of 20.3 fb−1. The signal is extracted using a maximum-likelihood fit of a discriminant which is based on the matrix element method and optimized in order to separate single-top-quark s-channel events from the main background contributions, which are top-quark pair production and W boson production in association with heavy-flavour jets. The measurement leads to an observed signal significance of 3.2 standard deviations and a measured cross-section of σs=4.8±0.8(stat.)−1.3+1.6(syst.) pb, which is consistent with the Standard Model expectation. The expected significance for the analysis is 3.9 standard deviations.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The measurement of the jet energy resolution is presented using data recorded with the ATLAS detector in proton-proton ...collisions at ... The sample corresponds to an integrated luminosity of 35 pb^sup -1^. Jets are reconstructed from energy deposits measured by the calorimeters and calibrated using different jet calibration schemes. The jet energy resolution is measured with two different in situ methods which are found to be in agreement within uncertainties. The total uncertainties on these measurements range from 20 % to 10 % for jets within |y|<2.8 and with transverse momenta increasing from 30 GeV to 500 GeV. Overall, the Monte Carlo simulation of the jet energy resolution agrees with the data within 10 %.
A search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented. The data were recorded in 2015 by the ATLAS experiment ...in s√= 13 TeV proton--proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 3.2 fb−1 of analyzed data. Results are interpreted within simplified models that assume R-parity is conserved and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 1.51 TeV for a simplified model incorporating only a gluino octet and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.03 TeV are excluded for a massless lightest neutralino. These limits substantially extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.
A
bstract
The results of a search for top squark (stop) pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The analysis is performed with ...proton-proton collision data at
s
= 8 TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20 fb
−1
. The lightest supersymmetric particle (LSP) is taken to be the lightest neutralino which only interacts weakly and is assumed to be stable. The stop decay modes considered are those to a top quark and the LSP as well as to a bottom quark and the lightest chargino, where the chargino decays to the LSP by emitting a
W
boson. A wide range of scenarios with different mass splittings between the stop, the lightest neutralino and the lightest chargino are considered, including cases where the
W
bosons or the top quarks are off-shell. Decay modes involving the heavier charginos and neutralinos are addressed using a set of phenomenological models of supersymmetry. No significant excess over the Standard Model prediction is observed. A stop with a mass between 210 and 640 GeV decaying directly to a top quark and a massless LSP is excluded at 95% confidence level, and in models where the mass of the lightest chargino is twice that of the LSP, stops are excluded at 95% confidence level up to a mass of 500 GeV for an LSP mass in the range of 100 to 150 GeV. Stringent exclusion limits are also derived for all other stop decay modes considered, and model-independent upper limits are set on the visible cross-section for processes beyond the Standard Model.
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